Process for converting methanol to alkyl ethers, gasoline, distillate and alkylate liquid hydrocarbons

ABSTRACT

A multistage process for producing ethers from lower aliphatic oxygenate feedstock, such as methanol. Feedstock is catalytically converted in a primary catalyst stage at elevated temperature in contact with zeolite catalyst to predominantly C 2  -C 5  lower olefins comprising isobutylene and isoamylene, by-product water and a minor amount of C 6   +  hydrocarbons, followed by fractionation of the C 2  -C 5  olefins to recover a C 2  -C 3  -rich recycle stream for further catalytic conversion in the primary stage. C 4  -C 5  olefins are passed to a second catalytic etherification stage for reaction of isoalkenes with methanol to produce methyl tertiary-butyl ether and methyl isoamylether. The second stage effluent may be fractionated to recover an ether product, C 5   +  hydrocarbon liquid product, and unreacted butenes. Advantageously, the unreacted butenes are further reacted wtih isoparaffin in a third catalytic stage under acid catalysis alkylation conditions, and fractionated to recover C 6   +  alkylate liquid, liquid hydrocarbon product. The ethers may be blended with at least one C 6   +  hydrocarbon to produce high octane gasoline.

BACKGROUND OF THE INVENTION

This invention relates to an integrated system for converting methanolto high octane liquid fuels, such as hydrocarbons. In particular, itprovides a continuous process for producing hydrocarbon fuel products orthe like by converting the aliphatic oxygenate feedstock catalyticallyto an intermediate lower olefinic stream, etherifying C₄ -C₅ olefins andalkylating isobutane or other isoparaffins with olefins to produce lightdistillate and/or gasoline products.

In order to provide an adequate supply of liquid hydrocarbons for use assynfuels or chemical feedstocks, various processes have been developedfor converting coal and natural gas to gasoline and distillate. Asubstantial body of technology has grown to provide oxygenatedintermediates, especially methanol. Large scale plants can convertmethanol or similar aliphatic oxygenates to liquid fuels, especiallygasoline. Demand for liquid hydrocarbons has led to the development ofprocesses for making liquid fuels by various synfuel techniques.

Increasing demand for high octane gasolines blended with lower aliphaticalkyl ethers as octane boosters and supplementary fuels has created asignificant demand for isoalkylethers, especially the C₅ to C₇ methylalkyl ethers, such as methyl tertiary butyl ether (MTBE) and tertiaryamyl methyl ether (TAME). It has been found advantageous to provide amethanol-based conversion unit which can produce the requiredintermediate chemicals.

Recent developments in zeolite catalysts and hydrocarbon conversionprocesses have created interest in utilizing olefins, for producing C₇ ⁺alkylate gasoline, etc. In addition to the basic work derived from ZSM-5type zeolite catalysts, a number of discoveries have contributed to thedevelopment of new industrial processes.

The medium pore ZSM-5 type catalysts are useful for converting methanol(MEOH) and other lower aliphatic alcohols or corresponding ethers tolower olefins and also for oligomerizing olefins. Particular interesthas been directed to a catalytic process for converting low costmethanol to valuable hydrocarbons rich in ethene and C₃ ⁺ alkenes.Various processes are described in U.S. Pat. No. 3,894,107 (Butter, etal.), 3,928,483 (Chang, et al.), 4,025,571 (Lago), 4,423,274 (Daviduk,et al.), 4,433,189 (Young), and 4,543,435 (Gould and Tabak),incorporated herein by reference. It is generally known that the MTOprocess can be optimized to produce a major fraction of C₂ -C₅ olefins.Prior process proposals have included a separation section to recoverethene and other light gases from by-product water and heavierhydrocarbons.

It is known that isobutylene may be reacted with methanol over an acidiccatalyst to provide methyl tertiary butyl ether (MTBE) and isoamylenesmay be reacted with methanol over an acidic catalyst to produce tertiaryamyl methyl ether (TAME). The catalyst employed is preferably an ionexchange resin in the hydrogen form. Substantially any acidic catalystmay be employed with varying degrees of success. That is, acidic solidcatalysts may be used; such as, sulfonic resins, phosphoric acidmodified kieselguhr, silica alumina and acid zeolites.

SUMMARY OF THE INVENTION

It has been discovered that methanol, DME or the like may be convertedto liquid fuels, particularly ethers and alkylates, in a multi-stagecontinuous process, with integration between the major process unitsproviding an alkylate product stream from C₄ ⁻ aliphatics produced byprimary stage zeolite catalysis. The initial stage MTO processhydrocarbon effluent stream, after by-product water separation andfractionation can be partially fed to an etherification stage and analkylation stage for conversion of C₄ -C₅ hydrocarbons to MTBE or TAME.Ethene and/or propene may be recovered by interstage separation forrecycle and co-reacted with methanol/DME or other C₁ -C₄ aliphaticoxygenates in the presence of ZSM-5 type catalysts.

In a preferred embodiment, the invention provides improved processes andapparatus for an integrated continuous technique for converting lowerolefins (e.g., butenes) to liquid alkylate hydrocarbons. A novel processhas been found for converting oxygenate feedstock comprising methanol toliquid hydrocarbons comprising the steps of

contacting the feedstock with zeolite catalyst in a primary catalyststage at elevated temperature to convert feedstock oxygenates tohydrocarbons comprising C₂ -C₅ olefins and C₆ ⁺ liquid hydrocarbons;

cooling and separating the primary stage effluent to recover a liquid C₆⁺ hydrocarbon stream and a light hydrocarbon stream rich in C₂ -C₅olefins;

compressing at least a portion of the olefinic light hydrocarbon streamto condense a liquid olefinic hydrocarbon stream rich in C₄ -C₅isoalkenes and recovering a gaseous stream rich in ethene and,optionally, propene;

reacting the isoalkenes with methanol in a secondary stageetherification zone by contacting the isoalkenes and methanol with anacid etherification catalyst to produce C₅ -C₆ methyl isoalkylethers;

fractionating the secondary stage effluent to obtain a liquid ether andC₅ ⁺ hydrocarbon stream and an olefinic stream rich in unreactedbutenes;

reacting the butene-rich olefinic stream with a tertiary alkane in acatalytic alkylation stage with acid alkylation catalyst to convert atleast a portion of olefins to alkylate gasoline; and

recycling ethene and/or propene in a gaseous stream to the primarycatalytic stage.

Other objects and features of the invention will be seen in thefollowing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow sheet showing the major unit operations andprocess streams;

FIG. 2 is a schematic representation of a preferred inter-stageseparation system; and

FIG. 3 is an alternative process flow sheet.

DESCRIPTION OF PREFERRED EMBODIMENTS

Numerous oxygenated organic compounds may be contained in the feedstockmaterial to be converted in the primary stage. Since methanol or itsether derivative (DME) are industrial commodities available fromsynthesis gas or the like, these materials are utilized in thedescription herein as preferred starting materials. It is understood bythose skilled in the art that MTO-type processes can employ methanol,dimethylether and mixtures thereof, as well as other aliphatic alcohols,ethers, ketones and/or aldehydes. It is known in the art to partiallyconvert oxygenates by dehydration, as in the catalytic reaction ofmethanol over gamma-alumina to produce DME intermediate. Typically, anequilibrium mixture (CH₃ OH +CH₃ OCH₃ +H₂ O) is produced by partialdehydration. This reaction takes place in either conversion of methanolto lower olefins (MTO) or methanol to gasoline (MTG).

Recent developments in zeolite technology have provided a group ofmedium pore siliceous materials having similar pore geometry. Mostprominent among these intermediate pore size zeolites is ZSM-5, which isusually synthesized with Bronsted acid active sites by incorporating atetrahedrally coordinated metal, such as Al, Ga, or Fe, within thezeolytic framework. These medium pore zeolites are favored for acidcatalysis; however, the advantages of ZSM-5 structures may be utilizedby employing highly siliceous materials or cystalline metallosilicatehaving one or more tetrahedral species having varying degrees ofacidity. ZSM-5 crystalline structure is readily recognized by its X-raydiffraction pattern, which is characterized by strong lines at d(A):11.1, 10.0, 3.84, and 3.72. The complete X-ray pattern and synthesis isdescribed in U.S. Pat. No. 3,702,866 (Argauer, et al.), incorporated byreference.

The zeolite catalysts preferred for use herein include the crystallinealuminosilicate zeolites having a silica-to-alumina ratio of at least12, a constraint index of about 1 to 12 and acid cracking activity(alpha) of about 1-50. Representative of the ZSM-5 type zeolites areZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-45 andZSM-50. ZSM-5 is disclosed and claimed in U.S. Pat. No. 3,702,886 andU.S. Pat. No. Re. 29,948; ZSM-11 is disclosed and claimed in U.S. Pat.No. 3,709,979. Also, see U.S. Pat. No. 3,832,449 for ZSM-12; U.S. Pat.No. 4,076,979. Also, see U.S. Pat. No. 3,832,449 for ZSM-12; U.S. Pat.No. 4,076,842 for ZSM-23; U.S. Pat. No. 4,016,245 for ZSM-35 and U.S.Pat. No. 4,046,839 for ZSM-38. The disclosures of these patents areincorporated herein by reference. A suitable catalyst for oxygenateconversion is HZSM-5 zeolite with alumina and/or silica binder. Certainof these medium pore shape selective catalysts are sometimes known asporotectosilicates or "pentasil" catalysts. ZSM-5 type catalysts areparticularly advantageous because the same material may be employed fordehydration of methanol to DME, conversion to lower olefins and recycleethylene conversion.

Other catalysts and processes suitable for converting methanol/DME tolower olefins are disclosed in U.S. Pat. No. 4,393,265 (Bonifaz), U.S.Pat. No. 4,387,263 (Vogt, et al.) and European Patent Application No.0081683 (Marosi, et al.). In addition to the preferred aluminosilicates,the borosilicate, ferrosilicate silica alumino phosphate (SAPO) and"silicalite" materials may be employed. While small pore (less than 5Å)zeolites, such as erionite, offretite, ZSM-34 etc., may be employed forolefin production, they often yield a large amount of ethene. Large pore(e.g. greater than 7Å) zeolites, such as mordenite, X, Y, etc., tend toproduce excessive coked deposits. ZSM-5 type catalysts are particularlyadvantageous because the same material may be employed for dehydrationof methanol to DME, conversion to lower olefins and recycle ethyleneconversion.

Primary Stage Operation

In this description, metric units and parts by weight are employedunless otherwise stated. Various reactor configurations may be used,including fluidized bed catalytic reactors, moving bed and fixed bedreactors.

The MTO process may be optimized by employing fluid bed primary stageconditions in the temperature range of about 425° C. to 550° C., apressure range of about 100 to 800 kPa and weight hourly space velocityrange of about 0.5 to 3.0 based on ZSM-5 equivalent catalyst andmethanol equivalent in the primary stage feedstock. Suitable equipmentand operating conditions are described in U.S. Pat. No. 4,579,999 (Gouldand Tabak), incorporated herein by reference.

The process is depicted in FIG. 1, wherein methanol-rich oxygenate isfed via conduit 10 to the oxygenate conversion system 20 in the primarystage and the primary stage effluent stream 22 is separated in a primaryfractionation system 24 to recover heavy liquid, by-product water,ethene-rich C₂ -C₃ light gas and C₄ -C₅ hydrocarbons, rich in butene andpentene isomers. The major amount of C₄ -C₅ olefins is fed to theetherification reactor system 30 for upgrading to ethers, especiallyMTBE and/or TAME. The ether products may be recovered separately viasecond fractionation system 34, or may be blended with the C₆ ⁺ gasolinestream.

The C₄ hydrocarbon stream from the secondary ether fractionation systemmay contain unconverted butylenes (C₄ =) and isobutane(i-C₄); however,the relative amounts of these components are not usually instoichiometric balance for alkylation. Accordingly, a stream ofisobutane is passed through the reactor system. Optionally, propene maybe passed from the primary stage to alkylation. Thus, the alkylationreactor system receives unreacted butylenes, mainly 1-butene and/or2-butene to alkylate isoparaffin derived from the reactor system orbrought in to the system.

In a preferred embodiment depicted in FIG. 2, the primary stage effluentis prefractionated before being sent to olefin upgrading units.Advantageously, the MTO effluent is received at about atmosphericpressure (e.g., 100-150 kPa) and compressed in plural stages to apressure of about 1500-3000 kPa and separated at about ambienttemperature (20°-80° C.). Olefinic liquids rich in C₄ ⁺ aliphatics maybe recovered from the final compressor stage and passed with the C₆ ⁺liquid hydrocarbon stream 1 to fractionation tower 124 where C₄ -C5alkenes are recovered. Isobutane may be optionally recycled from thealkylation stage as sorbent, as disclosed in copending U.S. patentapplication Ser. No. 779,369, filed Sept. 23, 1985 now U.S. Pat. No.4,634,798. A major portion of C₄ -C5 olefins may be sent toetherification from absorber 124. Referring to the process diagram ofFIG. 2, a gaseous feedstream 110 from an MTO reactor is compressedadiabatically in a series of compressors 102A, B, C and passed throughcorresponding coolers 103A, B, C and phase separators 104A, B, C torecover by-product water and condensed hydrocarbons containing variousamounts of C₃ -C5 aliphatics. A lower olefin intermediate stream 106 iscontacted with a liquid sorbent stream 108 in a countercurrent sorptiontower 124. Overhead vapor from tower 124 may be further purified incryogenic separation unit 125 to remove light hydrocarbon gas and C₄ ⁺components. The purified ethene and propene may be recovered or recycledto the primary stage MTO reactor for further conversion. The C₄ -C₅stream from unit 125 is rich in C₄ -C₅ isoalkenes, which may be upgradedto corresponding methyl ethers by passing the etherification reactor 30.

Heavy liquid rich in C₆ ⁺ hydrocarbons separated from the MTO processprimary effluent, is pressurized by pump 115 and fractionated in tower116 to recover a C₉ ⁺ aromatic-rich stream. The condensed overhead, richin CO₆ ⁺ aliphatic and aromatic components, may be recovered as product.Liguid sorbent (e.g., C₄ -C₉ hydrocarbons) from line 118 is fed via line108 to absorber unit 124. C₄ ⁺ components sorbed from the feed areremoved from column 124 as olefinic sorbate 119, which is feed, with orwithout fractionation, to the etherification reactor 30 for conversionto MTBE and TAME.

As shown by dashed line, an optional depertanizer tower 120 may beemployed to recover C₅ ⁺ components condensed from the compressorsection. The C₅ ⁻ overhead from tower 120 may be fed to theetherification reactor system for upgrading.

In the embodiment of FIG. 3, methanol feedstock is converted in MTO unit320, compressed and passed to fractrometer 324 to provide a C₆ ⁺ heavyliquid stream L. The light hydrocarbon vapor stream V is rich in etheneand/or propane separated from the primary stage effluent. The C₄ /C₅olefinic stream is etherified in reactor 330 and reaction effluent isfractionated to recover recycle methanol, C₅ ⁺ /blended product and a C₄stream contaiing unreacted butenes, a portion of which is recycled forfurther conversion in MTO reactor 320, where the isoalkenes areproduced.

The reaction of methanol with isobutylene and isoamylenes at moderateconditions with a resin catalyst is known technology, as provided by R.W. Reynolds, et al., The Oil and Gas Journal, June 16, 1975, and S.Pecci and T. Floris, Hydrocarbon Processing, Dec. 1977. An articleentitled "MTBE and TAME--A Good Octane Boosting Combo", by J. D. Chase,et al., The Oil and Gas Journal, Apr. 9, 1979, pages 149-152, discussesthe technology. The preferred catalyst is Amberlyst 15 sulfonic acidresin.

The ether product of reactor 330 comprising high octane ethers,unreacted olefins and methanol are fractionated in separation zone 334,maintained at a desired pressure, normally atmopsheric pressure, and atemperature within the range of 80° to 125° F., depending on theseparation desired. In one embodiment, C₅ and lower boiling unreactedolefins are separated along with unreacted methanol are separated andwithdrawn for recycle. Unconverted methanol and recycled olefins may beconverted in the MTO reactor desired olefin product. Unreacted C₅ ⁺olefins may also be separated from the high octane ethers and blended inpool gasoline. Thus, depending on the separating temperature andpressure conditions relied upon, the high octane ether product (TAME andMTBE) separated in zone either with or without C₅ plus olefins may bewithdrawn as a primary product of the combination process.

MTBE and TAME are known to be high octane ethers. The article by J. D.Chase, et al., Oil and Gas Journal, Apr. 9, 1979, discusses theadvantages one can achieve by using these materials to enhance gasolineoctane. Where a shortage of isobutylene and isoamylene exists andoxygenates are plentiful, the processing combination of the presentinvention contributes to improved octane gasoline product. The octaneblending number of MTBE when 10% is added to a base fuel (R+O=91) isabout 120. For a fuel with a low motor rating (M+O=83) octane, theblending value of MTBE at the 10% level is about 103. On the other hand,for an (R+O) of 95 octane fuel, the blending value of 10% MTBE is abut114, and for an (M+O) of 84 octane, the 10% blending value is about 100.

The alkylation process employed herein is a well known industrialtechnique for reacting alkenes with tertiary alkanes (isoparaffins),such as isobutane, isopentane, isohexane, etc. The resulting product isa C₇ ⁺ branched chain paraffinic material useful as aviation gasoline,jet fuel or the like. The alkylation of paraffins can be carried outeither thermally or catalytically; however, acid catalyst is preferred.Thermal or noncatalytic alkylation of a paraffin with an olefin iscarried out at high temperatures (about 500° C.) and pressures 21-41 MPa(3000-6000 psi). Under these conditions, both normal and isoparaffinscan be brought into reaction by a free-radical mechanism. Thermalalkylation is not known to be practiced commercially.

The catalytic alkylation of paraffins involves the addition of anisoparaffin containing a tertiary hydrogen to an olefin. The process isused in the petroleum industry to prepare highly branched paraffins,mainly in the C₇ to C₉ range, that are high-quality fuels. The overallprocess is complex, requiring control of operating conditions and ofcatalyst. The process conditions and the product composition depend onthe particular hydrocarbons involved.

The preferred alkylation processes are those brought about by theconventional protonic and Lewis catalysts. Propene can be brought intoreaction with an isoparaffin in the presence of either concentratedsulfuric acid or hydrogen fluoride. The heptanes produced by alkylationof isobutane with propene are mainly 2,3- and 2,4-dimethylpentane.Propene is alkylated preferably as a component of a C₃ -C₄ fraction HFcatalysts for alkylation of isobutane with 1- and 2-butenes give bothdimethylhexanes and trimethylpentanes. The product obtained fromalkylation of isobutane with isobutylene at low temperature (e.g., -25°C.) with hydrogen fluoride is 2,2,4-trimethylpentane.

During use the acid catalysts may become diluted with by-producthydrocarbons and as a result decrease in activity. Sulfuric acidconcentrations are maintained at about 90%. Hydrogen fluorideconcentrations of 80-90% are common, although the optimum concentrationdepends on the reaction temperature and reactor geometry. Operationbelow these acid concentrations generally causes incomplete conversionor polymerization. With sulfuric acid, the product quality is improvedwhen temperatures are reduced to the range of 0-10° C. Coolingrequirements are obtained by low temperature flashing of unreactedisobutane. With hydrogen fluoride, the reaction process is lesssensitive to temperature, and temperatures of 0-40° C. can be used. Someform of heat removal is essential because the heat of reaction isapproximately 14×10⁵ J/kg (600 Btu/lb) of butenes converted. Typically,the elevated pressure for alkylation by these acid catalysts is about1500 to 3000 kPa (200-300 psig).

In order to prevent polymerization of the olefin as charged, an excessof isobutane is present in the reaction zone. Isobutane-to-olefin molarratios of 6:1 to 14:1 are common, more effective suppression of sidereactions being produced by the higher ratios.

The typical alkylation reaction employs a two-phase system with a lowsolubility of the isobutane in the catalyst phase. In order to ensureintimate contact of reactants and catalyst, efficient mixing isprovided. This is important with sulfuric acid because of the lowsolubility of isobutane in the catalyst phase. In addition, the higherviscosity of the sulfuric acid requires a greater mixing energy toassure good contact. The solubility of the hydrocarbon reactants in thecatalyst phase is increased by the presence of the unsaturated organicdiluent held by the acid catalyst. This organic diluent also has beenconsidered a source of carbonium ions that promote the alkylationreaction.

For the hydrofluoric acid system, reactive i-C₄ H₈ readily alkylates togive an excellent product. The alkylation of pure 1-C₄ H₈ by itselfproceeds with considerable isomerization of the 1-C₄ H₈ to 2-C₄ H₈followed by alkylation to give a highly branched product. The presenceof i-C₄ H₈ accelerates the alkylation reaction and allows less time forolefin isomerization. Consequently, the reaction produces an alkylatewith a lowered antiknock value. For the sulfuric acid system, i-C₄ H₈tends to oligomerize and causes other side reaction products of inferiorquality; but, the isomerization of 1-C₄ H₈ to 2-C₄ H₈ proceeds morecompletely, thereby favoring formation of superior products. Thus, formixed olefin feeds such as described above, the two factors with bothcatalyst systems counteract each other to provide products of similarantiknock properties.

The olefin-producing MTO process may simultaneously generate isobutane,but the amount may be insufficient to alkylate the coproduced olefins. Asuitable outside source of isobutane is natural gas or a by-product ofmethanol-to-gasoline (MTG) processes.

Suitable alkylation processes are described in U.S. Pat. Nos. 3,879,489(Yurchak et al), 4,115,471 (Kesler), 4,377,721 (Chester) and in theKirk-Othmer Encyclopedia of Chemical Technology, Vol. 2, pp. 50-58 (3rdEd., 1978) John Wiley & Sons, incorporated herein by reference.

The combined processes are an effective means for converting oxygenatedorganic compounds, such as methanol, DME, lower aliphatic ketones,aldehydes, esters, etc., to valuable hydrocarbon products. Thermalintegration is achieved by employing heat exchangers between variousprocess streams, towers, absorbers, etc.

Various modifications can be made to the system, especially in thechoice of equipment and non-critical processing steps. While theinvention has been described by specific examples, there is no intent tolimit the inventive concept as set forth in the following claims.

We claim:
 1. A process for converting oxygenate feedstock comprisingmethanol to liquid hydrocarbons comprising the steps of(a) contactingthe feedstock with zeolite catalyst in a primary catalyst stage atelevated temperature and moderate pressure to convert feedstock tohydrocarbons comprising C₂ -C₅ olefins and C₆ ⁺ liquid hydrocarbons; (b)cooling and separating the primary stage effluent to recover a liquid C₆⁺ hydrocarbon stream and a light hydrocarbon stream rich in C₂ -C₅olefins including propylene and C₄ -C₅ isoalkenes; (c) compressing atleast a portion of the olefinic light hydrocarbon stream to condense aliquid olefinic hydrocarbon stream rich in C₄ -C₅ isoalkenes andrecovering a gaseous stream rich in ethene and propene; (d) reacting theisoalkenes with methanol in a secondary stage etherification zone bycontacting the isoalkenes and methanol with an acid etherificationcatalyst to produce C₅ -C₆ methyl isoalkylethers; (e) fractionating thesecondary stage effluent to obtain a liquid ether and C₅ ⁺ hydrocarbonstream and an olefinic C₄ stream rich in unreacted butenes andisobutane; (f) reacting the butene-rich olefinic stream from step (e)with isobutane in a catalytic alkylation stage in contact with acidalkylation catalyst to convert at least a portion of olefins to alkylategasoline; (g) recovering a propene-rich stream from step (c) andreacting said propene-rich stream with excess isobutane in step (f); and(h) recycling ethene and/or propene in a gaseous stream to the primarycatalytic stage.
 2. The process of claim 1 wherein primary stagefeedstock is converted over HZSM-5 catalyst to provide a light olefinichydrocarbon vapor stream comprising a major amount of C₃ -C₅ olefins anda minor amount of ethene.
 3. The process of claim 1 further comprisingthe step of compressing and fractionating gaseous effluent separatedfrom primary stage effluent to recover a recycle gas stream containingat least 90% of ethene from the primary catalytic stage.
 4. The processof claim 1 wherein the primary stage catalyst comprises ZSM-5 typezeolite and ethene is recycled to the primary stage at a rate of about 1to 10 parts ethene per 100 parts by weight of methanol equivalent in thefeedstock.
 5. The process of claim 1 wherein the light hydrocarbon vaporstream separated from the primary stage effluent is compressed in aplurality of compression stages to condense liquid olefinichydrocarbons, and wherein uncondensed compressed light hydrocarbons arefurther fractionated to recover a recycle stream containing at least 90mole percent ethene and propene.
 6. The process of claim 1 whereinisobutane is reacted with butene-1 and butene-2 in the alkylation stagein the presence of a liquid phase acid catalyst at a pressure of about1500 to 3000kPa.
 7. A multistage process for producing high octane fuelfrom lower aliphatic oxygenate feedstock which comprises the steps of(a)catalytically converting oxygenate feedstock in a primary catalyst stageat elevated temperature in contact with zeolite catalyst topredominantly C₂ -C₅ lower olefins comprising ethene, propene,n-butenes, isobutane, isobutylene and isoamylene, by-product water and aminor amount of C₆ ⁺ hydrocarbons; (b) fractionating the C₂ -C₅ olefinsto recover a C₂ -C₃ -rich recycle stream for further catalyticconversion in the primary stage and passing C₄ -C₅ olefins to a secondcatalytic etherification stage for reaction of isobutylene andisoamylene with methanol to produce methyl tertiary butyl ether andmethyl isoamylether, (c) fractionating second stage effluent to recoveran ether produce, C₅ ⁺ hydrocarbon liquid product, isobutane andunreacted n-butenes; (d) further reacting the unreacted n-butenes withisobutane in a third catalytic stage under acid catalysis alkylationconditions; (e) recovering C₇ ⁺ alkylate liquid; (f) recovering propenefrom step (b) fractionation and reacting said recovered propene withexcess isobutane in step (d); and (g) blending the ether with at leastone C₆ ⁺ hydrocarbon to produce high octane gasoline.